The present invention relates to a monitoring system for web breaks in a paper machine.
a number of cameras for imaging various positions of a monitored web;
digital image processing equipment for storing image data from a plurality of camera positions; and
selection means for choosing a focused picture region from the image data of various camera positions.
A monitoring system including cameras which image various positions of a monitored web, has been used earlier only for a subsequent analysis of web breaks. However, such a system has not been employed as an actual break sensor capable of detecting a web break. Typically this system has been used in conjunction with traditional break sensors used in a paper machine which are often unreliable, and in certain positions, such as at the wet end of a machine, these traditional sensors have been found generally completely useless.
This type of monitoring systems have been used earlier for a subsequent analysis of web breaks, but such systems have not been employed as an actual break sensor capable of detecting a web break. Traditional break sensors used in a paper machine are often unreliable and such traditional sensors are generally completely useless in certain positions, particularly at the wet end of a machine.
An object of the invention is to develop further a monitoring system of the above-described type to enable its use in lieu of traditional break sensors both in web break monitoring systems and in the actual control of a paper machine.
This object is achieved on a monitoring system for web breaks in a paper machine. A web is monitored by means of a number of cameras and the image data of various camera positions is used for compiling focused image regions. Camera-specific image processing equipment is adapted to compile image change data by comparing the changes between sequential images as far as the focused image region is concerned. The image change data is compared with a normal level of image change and an alarm message is delivered if the image change level has a deviation from the reference level which exceeds a preset threshold value. A break alarm is set off, in case the alarm message is delivered by image change data comparators of one or more pre-selected camera positions.
This object is achieved on the basis of the characterizing features set forth in the annexed claim 1. The non-independent claims disclose preferred embodiments of the invention.